U.S. Pat. No. 7,670,427 to Perez-Pena et al., incorporated herein by reference, discusses very fast setting of cementitious compositions for producing cement-based products such as cement boards achieved by adding an alkanolamine and a polyphosphate to a hydraulic cement such as portland cement and forming a slurry with water under conditions that provide an initial slurry temperature of at least 90° F. (32° C.). Additional reactive materials may be included such as high alumina cement, calcium sulfate and a pozzolan material such as class C fly ash.
U.S. Pat. No. 6,869,474 to Perez-Pena et al., incorporated herein by reference, discusses extremely fast setting of cementitious compositions for producing cement-based products such as cement boards achieved by adding an alkanolamine to hydraulic cement such as portland cement, and forming a slurry with water under conditions that provide an initial slurry temperature of at least 90° F. (32° C.). Additional reactive materials may be included such as high alumina cement, calcium sulfate and a pozzolanic material such as fly ash. Triethanolamine additions have been found to be a very powerful accelerator capable of producing formulations with relatively short final setting times with increased levels of fly ash and gypsum and without the need of calcium aluminate cements.
U.S. Pat. No. 8,070,878 to Dubey, incorporated herein by reference, discusses lightweight cementitious compositions for building products which have reactive materials comprising a blend of 40-80% portland cement, 0-20% high alumina cement, 0-7% calcium sulfate (gypsum) and 0-55% fly ash. The compositions can contain both fly ash and a triethanolamine, but the compositions do not use an alkali metal citrate or polyphosphate such as sodium trimetaphosphate (STMP).
U.S. Pat. No. 6,641,658 to Dubey, incorporated herein by reference, discusses rapid setting cementitious composition useful for making cement boards containing as reactive powders portland cement, pozzolan, high alumina cement, and insoluble calcium sulfate anhydrite, which provide reduced setting times compared to the prior-art cementitious compositions. The composition preferably comprises as a reactive powder blend 35 to 90 wt. % portland cement, 0 to 55 wt. % pozzolan, 5 to 15 wt. % high alumina cement, and 1 to 8 wt. % insoluble calcium sulfate anhydrite. Substitution of insoluble calcium sulfate anhydrite for conventional soluble gypsum (a dihydrate) increases the release of heat and decreases setting times, despite the use of very high amounts of pozzolanic materials, preferably fly ash.
US Patent Application Publication 20100040165 of Dubey, incorporated herein by reference, discusses the use of a fiberglass mesh scrim lattice reinforced cementitious board system which uses a lattice of fiber as a backbone structure for a portland cement mixture which contains alkanolamine, polyphosphate like STMP, and may include fly ash with water. In all instances, the slurry mixture contains fly ash and/or an alkanolamine.
Ettringite is a calcium aluminum sulfate compound having the formula Ca6Al2(SO4)3.32H2O or alternatively 3CaO.Al2O3.3CaSO4.32H2O. This is also written as Ca6Al2(SO4)3(OH)12.26H2O.
Ettringite forms as long needle-like crystals and provides rapid early strength to cement boards, for handling soon after being poured into a mold or over a continuous casting and forming belt.
There is a need for portland cement compositions which have final setting times typically less than about 4 to 7 minutes or less, which develop both high early stage and high long term compressive strength, but do not have migration of unwanted reactant such as alkanolamine to the surface of the panel. The final setting time is defined more generally, when the cementitious mixtures have set to the extent the cement-based products made thereof can be handled and stacked, although chemical reactions can continue for extended periods.